Oxidation of dibenzo-p-dioxin by lignin peroxidase from the basidiomycete Phanerochaete chrysosporium.

Abstract

Dibenzo-p-dioxin (I) was rapidly degraded in ligninolytic cultures of the basidiomycete Phanerochaete chrysosporium. Lignin peroxidase (LiP) oxidized I to generate the following products: catechol (V), dibenzo-p-dioxin-2,3-quinone (VIII), 2-hydroxy-5-(2-hydroxyphenoxy)-1,4-benzoquinone (IX), 4,5-dihydroxy-1,2-benzoquinone (X), 2-(2-hydroxyphenoxy)-1,4-benzoquinone (XI), 4-hydroxy-1,2-benzoquinone (XII), and 1,2-benzoquinone (XIII). Identical products were formed when the reaction was conducted under argon. No incorporation of 18O into products was observed when the reaction was conducted under 18O2. Oxidation of I in H(2)18O resulted in incorporation of two atoms of 18O into the quinone VIII. Nonenzymatic hydrolysis of the quinone (VIII) yielded catechol (V), IX and X. Hydrolysis of VIII in H(2)18O resulted in incorporation of 18O atoms into IX and X, whereas no incorporation of 18O atoms into V was observed. These results are explained by mechanisms involving the one-electron oxidation of I by LiP to produce the corresponding cation radical. Nucleophilic attack of water on the cation radical generates a 2-hydroxydibenzo-p-dioxin radical, which is oxidized to a delocalized cation. The attack of water at position C-4a of the 2-hydroxydibenzo-p-dioxin cation, followed by oxidation and C-O-C bond cleavage, lead to formation of the quinone (XI), which undergoes 1,4-addition of water and cleavage of the second C-O-C bond to generate V and XII.(ABSTRACT TRUNCATED AT 250 WORDS)